Power transmission device with thermally compensating bearing preload mechanism

ABSTRACT

A power transmission device includes a housing, a differential assembly having a case and a bearing assembly rotatably supporting the case within the housing. A preload is applied to the bearing assembly along a load path. A shim is positioned in the load path with the bearing assembly. The shim is constructed at least in part from a material having a predetermined coefficient of thermal expansion such that the shim is operable to compensate for different rates of thermal expansion in the components within the load path to maintain a desired bearing preload or a range of operating temperatures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/039,691 filed on Jan. 20, 2005, now U.S. Pat. No. 7,175,560. Thedisclosure of the above application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to power transmission devices and, moreparticularly, to a device operable to maintain a desired preload on abearing in an axle assembly.

It is known to rotatably support a differential case in an axle assemblyhousing using a pair of bearing assemblies. The bearing assemblies aretypically constructed to have an inner race, an outer race and aplurality of rollers positioned between the inner race and the outerrace. To achieve long bearing life during vehicle operation, it has beenfound that an axial preload positively affects bearing life.

Some axle assemblies include adjustment mechanisms operable to apply adesired preload to a bearing assembly. During axle assembly, anadjustment nut is typically rotated until a desired preload is met andthen the adjustment nut is fixed at that rotational position.Alternately, portions of the axle housing may be separated byapplication of an external force while the differential assembly andbearings are installed within the axle housing. After installation ofthe bearings and differential assembly, the force applied to the axlehousing is released to provide an axial load to the bearing assemblies.

While these methods have functioned well in the past to provide adesired bearing preload, improvements may be made. Specifically, aconcern regarding maintaining the desired bearing preload exists whenthe axle assembly is constructed using a variety of materials havingdifferent coefficients of thermal expansion. Specifically, some axleassembly housings are created using aluminum while the differential casemay be constructed from cast iron or steel. As the operating temperatureof the axle assembly varies, specific components expand and contract atdifferent rates. As such, the bearing preload set at a specifictemperature varies as the temperature deviates from the initial buildcondition.

SUMMARY OF THE INVENTION

The present invention includes a power transmission device including ahousing, a differential assembly having a case, and a bearing assemblyrotatably supporting the case within the housing. A preload is appliedto the bearing assembly along a load path. A shim is positioned in theload path with the bearing assembly. The shim is constructed at least inpart from a material having a predetermined coefficient of thermalexpansion in such that the shim is operable to compensate for differentrates of thermal expansion in the components within the load path tomaintain a desired bearing preload over a range of operatingtemperatures.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an exploded perspective view of a first embodiment drive axleconstructed in accordance with the teachings of the present invention;

FIG. 2 is a cross-sectional view of a portion of the axle assemblydepicted in FIG. 1;

FIG. 3 is a planar view of an exemplary thermally compensating shim;

FIG. 4 is a side view of the shim depicted in FIG. 3;

FIG. 5 is a cross-sectional view of the shim taken along line 5-5 shownin FIG. 3; and

FIG. 6 is a cross-sectional view of a portion of a second embodimentdrive axle assembly constructed in accordance with the teachings of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With reference to the drawings, a thermally compensating bearing preloadarrangement constructed in accordance with the teachings of theembodiment of the present invention is generally identified at referencenumber 8. The bearing arrangement includes a shim 10 operativelyassociated with an exemplary drive axle assembly 12. As particularlyshown in FIGS. 1 and 2, the drive axle assembly 12 is illustrated togenerally include an axle housing 14 for rotatably mounting a hypoidgear set including a pinion gear 16 and a ring gear 18 drivinglyinterconnected to a differential assembly 20. The differential assembly20 functions to transfer power to a pair of axle shafts (not shown)while compensating for any difference in axle shaft speed rotation asmay occur during a turn or other steering maneuver. In order tocompensate for a differential in axle shaft rotational speed, thedifferential assembly 20 includes a pair of pinion gears 24 and a pairof side gears 26 drivingly interconnected to the axle shafts. Tofacilitate proper function of the axle assembly 12, the differentialassembly 20 includes a case 27 rotatably mounted on a pair ofdifferential bearings 28. Each differential bearing 28 includes an innerrace 30, an outer race 32 and a plurality of rollers 34 positionedbetween the inner and outer races. The axle housing 14 includes twosemi-circular journals (not shown) for supporting approximately 180degrees of the circumference of each of the differential bearings 28. Apair of bearing caps 36 journally support the remaining approximateone-half of each of the differential bearings 28. Each bearing cap 36 ismounted to the axle housing 14 in a manner conventional in the art suchas via threaded fasteners.

To assure optimum differential bearing life and proper pinion gear toring gear engagement, a pair of adjustment nuts 38 are provided. Asshown in FIG. 2, each adjustment nut 38 has a first end 40 threadinglyengaged with the axle housing 14 and a second end 42 abuttingly engagedwith the differential bearing 28 such that rotation of the adjustmentnut 38 axially displaces the differential bearing 28. Each adjustmentnut 38 further includes a plurality of retention apertures or slots 44for receipt of a portion of an adjuster lock 46. Adjuster lock 46restricts adjustment nut 38 from rotation after a proper bearing preloadhas been applied.

FIG. 2 depicts shim 10 positioned between adjustment nut 38 and outerrace 32 of differential bearing 28. Shim 10 is operable to maintain adesired preload on differential bearing 28 through a range of operatingtemperatures. Specifically, shim 10 functions to compensate for changesin the size of components located within the load path that extendsthrough differential bearing 28 to thereby maintain a relativelyconsistent preload on differential bearing 28. For example, in theembodiment disclosed in FIG. 2, load is transferred in a load path thatextends through axle housing 14, adjustment nut 38, shim 10, outer race32, rollers 34 and inner race 30 and case 27. As previously mentioned,it has been found to be beneficial to maintain a compressive preloadbetween inner race 30 and outer race 32 of differential bearing 28during operation. Because materials having different coefficients ofthermal expansion can be located within the load path, a mechanism thataccommodates for differences in the thermal expansion of these materialscan be beneficial.

FIGS. 3-5 depict shim 10 in greater detail. Shim 10 includes asubstantially cylindrically-shaped body 48. Body 48 may be constructedby injection molding a polymeric material into a mold. The polymericmaterial may have a coefficient of thermal expansion greater than thecoefficient of thermal expansion of any other component placed withinthe differential bearing load path. In this manner, the material of shim10 increases at a greater rate than the material of the other componentswithin the differential bearing load path. Specifically, it iscontemplated that axle housing 14 may be constructed from a materialsuch as aluminum. The case 27 may be constructed from cast iron. Theinner race 30, the outer race 32 and the rollers 34 may be constructedfrom a hardenable machine steel. The axle housing 14, being constructedfrom aluminum, would have a higher coefficient of thermal expansion thanthe case 27, the inner race 30, the outer race 32 and the rollers 34.

If a drive axle assembly is constructed without shim 10 and thecomponents are at room temperature, the bearing preload will be within adesired range when each of the components are at that temperature. Ifthe temperature elevates during operation, axle housing 14 will expandat a greater rate than the other components. Based on the position ofthe components within the differential bearing load path, it iscontemplated that the differential bearing preload will decrease if thetemperature increases from the assembly temperature. Similarly, if axlehousing 14 reduces in size an amount greater than case 27 and bearingassembly 28 during a temperature decrease, a bearing preload increasewill likely occur. Therefore, the preload on differential bearing 28depends on the change in temperature between the operating temperatureand the assembly temperature. As previously described, shim 10 operatesto maintain the differential bearing preload within a desirable range bychanging size at a greater rate per change in temperature to account forthe change of size in axle housing 14 relative to the change in size ofthe other steel or iron components.

Shim 10 includes a first pair of plates 50 and a second pair of plates52 coupled to body 48. Each first plate 50 includes a first surface 54engaging a first surface 56 of body 48. A second surface 58 of firstplate 50 engages an end face 60 of adjustment nut 38. Similarly, eachsecond plate 52 includes a first surface 62 and an opposite secondsurface 64. First surface 62 engages a second surface 66 of body 48.Second surface 64 of second plate 52 engage an end face 68 of outer race32.

Body 48 includes a gate mark 70 formed during the injection molding andsubsequent body cooling processes. Gate mark 70 may be shaped as areduced thickness portion including a recessed first surface 72 offsetfrom first surface 56 as well as a recessed second surface 74 offsetfrom second surface 66. Depending on the manufacturing process used,first surface 72 and/or second surface 74 may not be recessed but mayprotrude outwardly beyond first surface 56 or second surface 66.Accordingly, first plates 50 are spaced apart from one another at thelocation of gate mark 70. Similarly, second plates 52 are spaced apartfrom one another at gate mark 70.

One skilled in the art will appreciate that while four plates are shownin the embodiment depicted in FIGS. 3-5, other embodiments having one,two or three plates are also contemplated. The embodiments with fewerplates are not outside the scope of the present invention. For example,if body 48 is manufactured in a manner such that gate mark 70 is alwaysat or below first surface 56 and second surface 66, two closed ring,washer-like plates may be implemented instead of the four platespreviously described. Additionally, another embodiment is contemplatedwhere only first surface 56 or second surface 66 of body 48 includes aplate coupled thereto. First plates 50 and second plates 52 function todistribute load across shim 10. If it is determined that the materialused to construct body 48 is of sufficient compressive strength, theshim plates located on one side of body 48 may be eliminated.

Regardless of number or shape, the plates may be coupled to body 48during the injection molding process or at a later time. Adhesives orother bonding techniques may be used to couple the body and plates aswell. Alternatively, the plates may be installed as separate componentsin contact with body 48.

An alternate embodiment axle assembly 200 is depicted at FIG. 6. Axleassembly 200 is substantially similar to axle assembly 12 except thatadjustment nuts are not utilized to impart the differential bearingpreload. Like elements will retain their previously introduced referencenumerals.

Axle assembly 200 includes differential bearings 28 rotatably supportingcase 27 as previously described with reference to drive axle assembly12. However, adjustment nuts 28 and adjuster locks 36 are not requiredin the embodiment disclosed in FIG. 6. To impart a desirabledifferential bearing preload, portions of an axle housing 202 aredeflected outwardly to increase the size of an opening 204 within axlehousing 202. Differential assembly 20 and differential bearings 28 areplaced within opening 204 while the opening is being enlarged bymechanical force. After the differential assembly 20, along withdifferential bearings 28, are properly positioned within axle housing202, the force enlarging opening 204 is released. The axle housing 202springs back to an undeformed shape and imparts the desired differentialbearing preload, To account for variation in machining of the variousaxle assembly components and to achieve the desired differential bearingpreload, a spacer 206 may be placed within the bearing preload path.Alternatively, a family of shims similar to shim 10 may be constructedwith different thicknesses to provide the desired initial bearingpreload as well as a mechanism for maintaining the bearing preload overvarying operating temperatures.

FIG. 6 depicts shim 10 being positioned between outer race 32 and axlehousing 202. One skilled in the art will appreciate that a shim similarto shim 10 may alternatively be positioned between inner race 30 anddifferential case 27 without departing from the scope of the invention.Furthermore, the materials discussed were merely exemplary and it shouldbe appreciated that the thermally compensating preload arrangementpreviously described is operable to account for dissimilar thermalcoefficients of expansion between any number of materials.

Furthermore, the foregoing discussion discloses and describes merelyexemplary embodiments of the present invention. One skilled in the artwill readily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationsmay be made therein without department from the spirit and scope of theinvention as defined in the following claims.

1. An axle assembly, comprising: an axle housing; a differentialassembly having a case; first and second laterally spaced bearingsrotatably supporting said case in said housing; a preload mechanism forapplying a preload to at least one of said first and second bearingsalong a load path defined between said housing and said case; and a shimpositioned in said load path between said first bearing and one of saidhousing and said case, said shim including a body, a first metal loaddistributing element and a second metal load distributing element, saidfirst metal load distributing element is coupled to a first side of saidbody and said second metal load distributing element is coupled to asecond side of said body with one of said first and second metal loaddistributing elements abutting said first bearing, said body is formedof a material having a predetermined coefficient of thermal expansionand is operable to at least partially compensate for different rates ofthermal expansion in a plurality of components located within said loadpath to maintain said preload, wherein at least one of said first andsecond metal load distributing elements does not extend fully aroundsaid body.
 2. The axle assembly of claim 1 wherein said body is formedof plastic.
 3. The axle assembly of claim 1 wherein said shim includes athird metal load distributing element that is coupled to said first sideof said body and is spaced apart from said first metal load distributingelement.
 4. The axle assembly of claim 3 wherein said shim includes afourth metal load distributing element that is coupled to said secondside of said body.
 5. The axle assembly of claim 4 wherein said secondand fourth metal load distributing elements are spaced apart from oneanother.
 6. The axle assembly of claim 1, wherein said first bearingincludes an inner race, an outer race and a plurality of roller elementspositioned between said inner and outer races, and wherein said shimengages one of said inner and outer races.
 7. The axle assembly of claim6 wherein said shim engages said outer race of said first bearing andsaid housing.
 8. The axle assembly of claim 1 wherein said housing isconstructed from a material having a coefficient of thermal expansiongreater than a coefficient of thermal expansion of a material from whichsaid case is constructed.
 9. The axle assembly of claim 8 wherein saidshim is constructed from at least one material having a coefficient ofthermal expansion greater than a coefficient of thermal expansion of amaterial from which said housing is constructed.
 10. The axle assemblyof claim 1 wherein said preload mechanism includes a threaded memberthat is threadably coupled to said housing, said threaded member beingrotatable about and axially movable for adjusting said preload appliedby said shim on said first bearing.
 11. The axle assembly of claim 1further comprising a second shim positioned in said load path betweensaid second bearing and one of said housing and said case.
 12. The axleassembly of claim 11 wherein said preload mechanism includes anadjustment member moveable relative to said housing and said firstbearing so as to apply said preload to said first bearing.
 13. The axleassembly of claim 12 wherein said preload mechanism further Includes asecond adjustment member operable for applying said preload to saidsecond bearing.
 14. The axle assembly of claim 11 wherein said secondshim is formed of a material having a coefficient of thermal expansiongreater than a coefficient of thermal expansion for a material fromwhich said housing Is constructed.
 15. An axle assembly, comprising: ahousing; a differential assembly having a case; a bearing rotatablysupporting said case for rotation In said housing, said bearing beingpositioned in a load path defined between said housing and said casealon which a compressive preload is applied to said bearing; and a shimpositioned in said load path between said bearing and one of saidhousing and said case, said shim including a body, a first metal plate,a second metal plate and a third metal plate, said first metal platebeing coupled to a first side of said body, said second metal platebeing coupled to a second side of said body, said third metal platebeing coupled to said first side and spaced apart from said first metalplate, at least one of the first, second and third metal plates abuttingsaid bearing, wherein said body is formed of a material having apredetermined coefficient of thermal expansion and is operable to atleast partially compensate for different rates of thermal expansion in aplurality of components within said load path to maintain saidcompressive preload over a predetermined range of operatingtemperatures.
 16. The axle assembly of claim 15, further comprising: asecond bearing coupled to said housing and rotatably supporting saidcase on a side of said case opposite said first bearing, said secondbearing being positioned in said load path; and a second shim positionedin said load path between said second bearing and said housing or saidcase.
 17. The axle assembly of claim 16 wherein second shim isconstructed from a material and configured to cooperate with said firstshim to compensate for different rates of thermal expansion incomponents within said load path to maintain said compressive preloadover said predetermined range of operating temperatures.
 18. The powertransmission device of claim 15 wherein said body is formed of plastic.19. The axle assembly of claim 18 wherein said body is substantiallycylindrically shaped and includes an aperture extending therethrough.20. The axle assembly of claim 19 wherein said shim includes a fourthmetal plate that is coupled to said second side of said body.
 21. Theaxle assembly of claim 15 wherein said bearing includes an inner race,an outer race and a plurality of elements positioned between said innerand outer races, and wherein said shim engages one of said inner andouter races.
 22. The axle assembly of claim 21 wherein said shim engagessaid outer race of said bearing and said housing.
 23. The axle assemblyof claim 15 wherein said shim is constructed from at least one materialhaving a coefficient of thermal expansion greater than a coefficient ofthermal expansion of a material from which said housing is constructed.24. The axle assembly of claim 15 further including a threaded memberthat is threadably coupled to said housing, said threaded member isrotatable and axially movable to apply said preload to said bearing. 25.A drive axle assembly comprising: an axle housing; an input shaft havinga pinion gear and which is rotatably supported in said axle housing by afirst bearing; a differential assembly having a case, a ring gear fixedto said case that is meshed with said pinion gear, and second and thirdbearings rotatably supporting said case in said housing; and a shimpositioned between said axle housing and one of said first, second andthird bearings, said shim including a body, a first metal loaddistributing element and a second metal load distributing element, saidfirst metal load distributing element is coupled to a first side of saidbody and said second metal load distributing element is coupled to asecond side of said body opposite said first side, one of said first andsecond metal load distributing elements abuts said first bearing, saidbody is formed of a material having a predetermined coefficient ofthermal expansion operable to at least partially compensate fordifferent rates of thermal expansion in components within a load path tomaintain said preload over a predetermined range of operatingtemperatures, wherein at least one of said first and second metal loaddistributing elements does not extend fully around said body.